JPH0443610A - Voltage-dependent nonlinear resistor ceramic composition and method for producing varistor - Google Patents

Abstract

PURPOSE:To improve characteristics of permittivity, varistor voltage, surge yield strength, etc. by preparing ceramic composition by using the respective specified quantities of component wherein a part of Sr of SrTiO3 is substituted by Ba, component composed of two kinds of different metal oxide, and component wherein BaTiO3 and SiO2 are mixed and baked. CONSTITUTION:Main component is constituted by containing the following; 90.000-99.998 mol% of (Sr1-xBax)aTiO2 (0.001<=x<=0.300, 0.950<=a<=1.000), 0.001-5.000 mol% of at least one ore more kinds out of Nb2O5, Ta2O5, WO3, etc. and 0.001-5.000 mol% of at least one or more kinds out of Al2O3, Sb2O3, BaO, etc. Admixture is made by baking, at 1200 deg.C or higher, mixture composed of 60.000-32.500 mol% of BaTiO3 and 40.000-67.5 mol% of SiO2. Ceramic composition is prepared by using 100 wt.% of the main component and 0.001-10.000 wt.% of the admixture. Thereby varistor voltage is lowered; stability of characteristics is increased because the uniformity of grain diameter is improved; especially surge yield strength is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a voltage having capacitor characteristics and varistor characteristics to protect semiconductors and circuits of equipment from abnormal high voltages, noise, static electricity, etc. generated in electrical equipment and electronic equipment. The present invention relates to a dependent nonlinear resistor ceramic composition and a method for manufacturing a varistor.

Conventional technology Conventionally, SiC varistors and Z
nO type varistors are used. The voltage-current characteristics of such a varistor can be approximately expressed as in the following equation.

α 1−(V/C) Here, ■ is a current, ■ is a voltage, C is a constant specific to the varistor, and α is a voltage-current nonlinear index.

The α of SiC varistors is about 2 to 7, and the α of some ZnO-based varistors is as high as 50. Such varistors have excellent performance in absorbing relatively high voltages, but due to their low dielectric constant and small inherent capacitance, they are hardly capable of absorbing relatively low voltages below the varistor voltage. It has no effect, and the dielectric loss tan δ is as large as 5 to 10%.

On the other hand, semiconductor capacitors with an apparent dielectric constant of about 5×10' and a tan δ of about 1% are used to remove these low voltage noises. However, when a voltage or current exceeding a certain limit is applied to such a semiconductor capacitor due to a surge or the like, the capacitance decreases or is destroyed, and the capacitor no longer fulfills its Il function.

Recently, products containing 5rTiO* as the main component and having both varistor and capacitor properties have been developed, and are used in ICs and L
It is used to protect semiconductor devices such as SI.

Invention tries to solve! ! The element with the functions of both a varistor and a capacitor whose main component is 5rTiO mentioned above has a dielectric constant about 10 times higher than that of a ZnO-based varistor, but its α and surge resistance are small, and its characteristics deteriorate when the varistor voltage is lowered. It had the disadvantage of being susceptible to deterioration.

Therefore, an object of the present invention is to provide a voltage-dependent nonlinear resistor ceramic composition that has a large dielectric constant, a low varistor voltage, a large α, and a large surge withstand capacity, and a method for manufacturing the varistor.

Means for Solving the Problems In order to solve the above problems, in the present invention, (Sr+-
xBaJ-Ti03 (0,001≦X≦0.300.0
．． 950≦a<1.0oo) (hereinafter referred to as the first component) is 90.000 to 99.998so1χ, NbzOs1
DingazOs, WOi, DyzOz, YzOz, 1. az
03°Ce01. S@tOs, PrhOx, NdxOs
At least one type L (hereinafter referred to as the second component) of 0.001 to 5.000so1χ, Alt03,5bJ
t, BaO, BeO, PbO, B20x, CryOiF
etOi, CdO, KzO, CaO, Cox03. Cu
O, CuJ, Li2O, LiFMgO, Mn0z, MO
Ot, NaJ, NaF, N! 0. RJOi, 5eOz,
AgJSiOl, SiC, SrO, TltOi, T
haw, Ti0z, zOs, 81 z(L+, Z
At least one type of n0ZrO□, Snow (
(hereinafter referred to as the third component) from 0.001 to 5.0 OOsol
100 parts by weight of the main component containing χ and BaTi0:+
60. OOO~32.500molχ, 5iOz
A voltage-dependent nonlinear resistor comprising 0.001 to 10.000 parts by weight of an additive (hereinafter referred to as the fourth component) obtained by firing a mixture of 40.000 to 67.5i+olχ at 1200 to 1300°C. The aim is to solve the problem by obtaining a porcelain composition.

In addition, a composition consisting of the above main ingredients and additives was added to 1100
Let us provide a method for manufacturing a varistor fired at a temperature of 1200°C or higher, and a method for manufacturing a varistor fired at a temperature of 1200°C or higher in a reducing atmosphere, and then at a temperature of 900 to 1300°C in an oxidizing atmosphere. That is.

Effect In the above invention, the first component is the main component, and 5r
By substituting a portion of Sr in TiOs with Ba, a high resistance layer formed at grain boundaries becomes strong against surges. In addition, by making the stoichiometric ratio of A sites such as Sr and Ba and the stoichiometric ratio of B sites such as Ti excessive,
It is possible to lower the resistance inside the grains and increase the dielectric constant of the dielectric formed at the grain boundaries. Further, the second component is mainly a metal oxide that promotes semiconducting of the first component. Further, the third component contributes to improving the dielectric constant, α, and surge resistance, and the fourth component is effective in reducing the varistor voltage and improving the dielectric constant. In particular, the fourth component has a melting point of 12
Since it is relatively low at 30 to 1250°C, it turns into a liquid phase when fired at a temperature around the melting point, which promotes the reactions of other components and the growth of particles. Therefore, the third component is likely to be segregated in the grain boundary portion, and the resistance of the grain boundary is likely to be increased, thereby improving the varistor function and the capacitor function. In addition, since grain growth is promoted, the varistor voltage is lowered, and the uniformity of the grain size is improved, resulting in improved stability of characteristics, and in particular, improved surge resistance.

Example The present invention will be specifically explained below with reference to Examples.

First, BaTi01.5iOt was weighed at various composition ratios as shown in Table 1 below, and 20
Mix for 0 hours.Next, after drying, bake at various temperatures as shown in Table 1 below, grind again for 20 hours with a ball mill, etc., dry, and use as the fourth component. The components, second component, third component, and fourth component were weighed to have the composition ratio shown in Table 1 below, mixed for 24 hours using a ball mill, etc., dried, and an organic binder such as polyvinyl alcohol was added to 10 wtχ After adding and granulating, 10φ×11(-
), and fired at 1000°C for 100°C to remove the binder.Next, it was fired at various temperatures and times as shown in Table 1 (first firing), and then reduced Baking is performed at various temperatures and times in an atmosphere, for example, a gas of N, :H, = 9:1 (second firing).Furthermore, after that,
Firing is performed in an oxidizing atmosphere at various temperatures and times (third firing).

(Margins below) A conductive paste such as Ag was applied by screen printing on both sides of the sintered body 1 shown in FIGS. 1 and 2 obtained in this way, leaving the outer periphery, and
The electrodes 2 and 3 are formed by firing at 5 m1n. Next, lead wires (not shown) are attached using solder or the like, and a resin such as epoxy is applied. The characteristics of the device thus obtained are shown in Table 2 below.

In Table 2, the dielectric constant is calculated from the capacitance at IKHz, and α is α=1/log(V z+*a/V +5A)
(However, V IaA, V I., are 1 mA, 1
This is the voltage applied to both ends of the element when a current of 0 mA is applied. ) was evaluated. Further, the surge resistance was evaluated based on the maximum pulse current value when the rate of change in VImA after applying the pulse current was within ±10%.

(Hereinafter, blank space) In the present invention, (Sr+-xBax) a of the first component
The reason for defining the range of X in Tios is that if X is smaller than 0.001, it will not be effective, and if it exceeds 0.300, lattice defects will be less likely to occur, so semiconductor formation will not be promoted, and Ha will be present at grain boundaries. This is because the structure becomes non-uniform because it precipitates as a single phase, and v1□ becomes too high, deteriorating the properties. In addition, the range of a was specified because if it is smaller than 0.950, crystals of Ti alone will precipitate and the structure will become non-uniform, resulting in deterioration of characteristics, and if it exceeds 1.000, the dielectric constant of the dielectric will deteriorate. This is to do so. Furthermore, the second component is 0.001■
If it is less than 5.000 molχ, it will not be effective, and if it exceeds 5.000 molχ, it will segregate at the grain boundaries, suppress the increase in resistance of the grain boundaries, and form a second phase at the grain boundaries, resulting in deterioration of properties.

Furthermore, if the third component is less than 0.001 molχ, it does not exhibit any effect, and if it exceeds 5.000 molχ, it segregates at grain boundaries and forms a second phase, resulting in deterioration of properties. The fourth component is a substance having the lowest melting point in the phase diagram of the two-component system of BaTiO3 and SiO□, and has a high melting point outside this range. Furthermore, if the amount of the fourth component added is less than 0.001 parts by weight, no effect will be shown;
If it exceeds 0.000 parts by weight, the grain boundary resistance increases, but the width of the grain boundaries also increases, resulting in a decrease in capacitance and V
ImA becomes high, making it vulnerable to surges. Furthermore, the firing temperature of the fourth component is specified because the temperature at which the fourth component having a low melting point is synthesized is 1200° C. or higher. In addition, the temperature of the first firing was specified because the melting point of the fourth component is 1230 to 1250°C, so
This is because when fired at a temperature of 00"C or higher, the fourth component enters a state close to a liquid phase, promoting sintering.
This is because there is no liquid phase sintering effect due to the fourth component if it is less than that. The temperature for the second firing was set at 1200°C.
This is because if it is less than that, the sintered body after the first firing will not be sufficiently reduced, and both the varistor characteristics and the capacitor characteristics will deteriorate.

In addition, the temperature for the third firing was specified because if it is less than 900°C, the resistance of the grain boundaries will not increase sufficiently. This is because the varistor characteristics deteriorate if A becomes too low, and 130
This is because if the temperature exceeds 0°C, the capacitance becomes too small and the capacitor characteristics deteriorate. Furthermore, it was confirmed that the same effect can be obtained whether the atmosphere for the first firing is an oxidizing atmosphere or a reducing atmosphere.

In addition, in this example, regarding the combination of additives, (Sr+-'IIBax)aTios (
0,001≦X≦0.300.0.950≦a <1.
000), NbtOs, Taxes, W as the second component
O3, DyzOz, Y! O! + La2O2, CeOz
lSmtOxPrhOll, NdtOs, AIz03. as the third component. PbO, Cr1Os.

F e J 31 CdO+ K tO+ Coxes
＋Cub、CutOLl! 011 MgO+
MnOxMooi, NjO,5eOz, AgtO,S
iC, TlgOs, Zr0z, BaT as the fourth component
Although only i0.5ift is shown, other combinations include 5b103. Bad.

BeO, BtOi+CaO, LiF, NazO, NaF
, RhzO3+510g, SrO.

Th0t, Ti0z, VtOs, BizOs, ZnO,
It was confirmed that similar effects could be obtained by combining compositions using Snow.

Also, for the second component and the fourth component, 2
In addition, f! Approved.

Note that the first component, second component, third component, and fourth component are 11
Even by firing at temperatures above 00°C, the fourth component turns into a liquid phase, which promotes the reaction of other components and the growth of particles, making it easier for the third component to segregate at grain boundaries.
This has the effect of making grain boundaries more likely to have high resistance, improving varistor function and capacitor function.

Effects of the Invention As shown above, according to the present invention, due to the liquid phase sintering effect of the fourth component, the varistor voltage is low due to the large particle size, the dielectric constants ε and α are large, and the variation in particle size is small. Therefore, surge current flows uniformly through the element, and Ba
This effectively increases the resistance of the grain boundaries, resulting in the effect of increasing surge resistance.

[Brief explanation of the drawing]

FIG. 1 is a top view showing an element according to the invention, and FIG. 2 is a sectional view showing the element according to the invention. 1... Sintered body, 2, 3... Electrode. Name of agent: Patent attorney Shigetaka Awano

Claims (3)

[Claims] (1) (Sr_1_−_xBa_x)_aTiO_3(
0.001≦x≦0.300, 0.950≦a<1.0
00) to 90.000 to 99.998 mol%, Nb_
2O_5, Ta_2O_5, WO_3, Dy_2O_3
, Y_2O_3, La_2O_3, CeO_2, Sm_
0.001 to 5.000 mol% of at least one of 2_3, Pr_6O_1_1, and Nd_2O_3
, Al_2O_3, Sb_2O_3, BaO, BeO,
PbO, B_2O_3, Cr_2O_3, Fe_2O_
3, CdO, K_2O, CaO, Co_2O_3, Cu
O, Cu_2O, Li_2O, LiF, MgO, MnO
_2, MoO_3, Na_2O_3, NaF, NiO,
Rh_2O_3, SeO_2, AG_2O, SiO_2
, SiC, SrO, Tl_2O_3, ThO_2, Ti
O_2, V_2O_5, Bi_2O_3, ZnO, Zr
At least one of O_2 and SnO_2 is added to 0.
Main component 100 containing 001 to 5.000 mol%
Weight parts and BaTiO_3 60.000 to 32.50
0 mol%, SiO_2 40.000-67.5 mo
A voltage-dependent nonlinear resistor ceramic composition comprising 0.001 to 10.000 parts by weight of an additive obtained by firing a mixture consisting of 1% and 1% by weight at 1200°C or higher. (2) (Sr_1_−_xBa_x)_aTiO_3(
0.001≦x≦0.300, 0.950≦a<1.0
00) to 90.000 to 99.998 mol%, Nb_
2O_5, Ta_2O_5, WO_3, Dy_2O_3
, Y_2O_3, La_2O_3, CeO_2, Sm_
0.001 to 5.000 mol of at least one of 2O_3, Pr_6O_1_1, Nd_2O_3
%, Al_2O_3, Sb_2O_3, BaO, BeO
, PbO, B_2O_3, Cr_2O_3, Fe_2O
_3, CdO, K_2O, CaO, Co_2O_3, C
uO, Cu_2O, Li_2O, LiF, MgO, Mn
O_2, MoO_3, Na_2O, NaF, NiO, R
h_2O_3, SeO_2, AG_2O, SiO_2,
SiC, SrO, Tl_2O_3, ThO_2, TiO
_2, V_2O_5, Bi_2O_3, ZnO, ZrO
_2, at least one type of SnO_2 0.0
100 parts by weight of the main component containing 01 to 5.000 mol% and BaTiO_3 60.000 to 32.500
mol%, SiO_2 40.000-67.5 mol
A method for manufacturing a varistor, characterized in that a composition comprising 0.001 to 10.000 parts by weight of an additive is obtained by firing a mixture of 10% and 10% by weight at 1200°C or higher, and a composition comprising 0.001 to 10.000 parts by weight of an additive is fired at 1100°C or higher. (3) (Sr_1_−_xBa_x)_aTiO_3(
0.001≦x≦0.300, 0.950≦a<1.0
00) to 90.000 to 99.998 mol%, Nb_
2O_5, Ta_2O_5, WO_3, Dy_2O_3
, Y_2O_3, La_2O_3, CeO_2, Sm_
0.001 to 5.000 mol of at least one of 2O_3, Pr_6O_1_1, Nd_2O_3
%, Al_2O_3, Sb_2O_3, BaO, BeO
, PbO, B_2O_3, Cr_2O_3, Fe_2O
_3, CdO, K2O, CaO, Co_2O_3, Cu
O, Cu_2O, Li_2O, LiF, MgO, MnO
_2, MoO_3, N_2o, NaF, NiO, Rh_
2O_3, SeO_2, Ag_2O, SiO_2, Si
C, SrO, Tl_2O_3, ThO_2, TiO_2
, V_2O_5, Bi_2O_3, ZnO, ZrO_2
, at least one type of SnO_2 at 0.001
100 parts by weight of the main component containing ~5.000 mol% and 60.000~32.500 mo of BaTiO_3
1%, SiO_2 40.000 to 67.5 mol% is baked at 1200°C or higher and has no additives.
．． 001 to 10.000 parts by weight,
After firing at 100℃ or higher, 1200℃ in a reducing atmosphere
℃ or higher, and then heated to 900-13℃ in an oxidizing atmosphere.
A method for manufacturing a varistor, characterized in that the varistor is fired at 00°C.